Jet-nozzle arrangements with outlet area varying means



Aug. 6, 1957 N. BATTLE ETAL JET-NOZZLE ARRANGEMENTS WITH OUTLET AREAVARYING MEANS Filed June 16, 1954 6 Shee ts-Sheet l Aug-6,1957 N. BATTLEETAL 2,801,516

JET-NOZZLE ARRANGEMENTS WITH OUTLET AREA VARYING MEANS Filed June 16,1954 e Sheets-Sheet z 55 J g 6&5 59 60 y as 9? 50 w flfia 92a 9210695924 yaw 7 9293 4 1957 N. BATILE EI'AL 2,801,516

JET-NOZZLE ARRANGEMENTS WITH OUTLET AREA VARYING MEANS Filed June 1s,19s4 e Sheets-Sheet 5 Aug. 6, 1957 N. BATTLE ETAL 2,801,516 JET-NOZZLEARRANGEMENTS WITH 01mm AREA mama MEANS 6 Sheets-Sheet 6 Filed June 16,1954 2,801,516 P e A g- 1.957.

Units SW68 Pa fi i JET-NOZZLE ARRANGEMENTS WITH OUTLET AREA VARYINGMEANS Norman Battle, Chilwell, and Norman Robert Robinson, Quarndon,England, assignors to Rolls-Royce Limited, Derby, England, a Britishcompany Application June 16, 1954, Seriai No. 437,216 Claims priority,application Great Britain June 18, 1953 8 Claims. (Cl. 6035.6)

This invention comprises improvements in or relating to jet nozzlearrangements such as are employed in connection with gas-turbine enginesfor reaction propulsion purposes.

It is usual in jet nozzle arrangements employed with gas-turbine enginesto arrange the effective area of the outlet orifice for the exhaustgases from the associated gas-turbine engine to be variable, so that,for instance, when the engine is fitted with after-burner equipment theeffective area of the jet nozzle arrangement can be increased thereby toavoid overheating of the engine turbine.

This inventon has for an object to provide an improvedvaliable-orifice-area jet nozzle arrangement.

According to one aspect of this invention, there are provided aplurality of pivoted nozzle elements by means of which the effectivearea of the outlet orifice can be varied, and operating means by whichthe nozzle elements are interconnected and adapted to move the nozzleelements from one position to another, said operating means beingmounted on the movable nozzle elements themselves.

Preferably, the operating means comprise a plurality of telescopingmechanisms, each of which mechanisms has a pair of elements adapted totelescope with respect to one another along a line which is directedcircumferentially of the jet nozzle, one of said elements beingconnected to one nozzle element and the second of said telescopingelements being connected to an adjacent nozzle element.

In one arrangement according to this aspect of the invention, theoperating means are fluid-operated rams which havecircumferentially-directed lines of action, one part of the ram beingattached to one nozzle element and a second and relatively movable partof the ram being-attached to an adjacent nozzle element. With such anarrangement on expansion of the ram the nozzle elements may convenientlybe made to rock outwardly to increase the effective orifice area and oncollapse of the rams the nozzle elements may be made to rock inwardly todecrease the effective orifice area.

In one construction the nozzle elements are axially elongated and arepivoted adjacent their forward ends and the operating means arehydraulic rams and the cylinders of the rams are attached in pairs toalternate nozzle elements and the pistons of the rams are con nectedwith the remaining nozzle elements through pivoted links. With such aconstruction there are conveniently a relatively large number of nozzleelements; for instance 16 such interconnected nozzle elements may beemployed. In addition to these interconnected nozzle elements there maybe provided sealing nozzle elements which overlap the circumferentialedges of the main nozzle elements to prevent leakage of hot gas from theduct formed by the nozzle elements, and the parts of the sealing nozzleelements which overlap the main nozzle elements may be located withrespect to themain nozzle elements adjacent one end thereof, say theforward ends thereof.

Conveniently where a large number of pivotednozzle elements are providedmeans is also provided to constrain the pivoted nozzle elements to movethrough equal angular extents. In one particular arrangement such meanscomprises pairs of links, each pair being between a pair of adjacentnozzle elements and one link of each pair being pivoted to acorresponding one of the nozzle elements, the pairs being pivotedtogether at their opposite ends. The pivotal axes of the connectionsbetween the links and the nozzle elements are preferably radial.

According to another aspect of this invention, there is provided a jetnozzle arrangement which is readily attachable to and detachable from anassociated aircraft and jet pipe structure.

In one arrangement according to this aspect of the invention, there isprovided a mounting structure which is adapted to encircle thedownstream end of the jet pipe leading from an associated gas-turbineengine, and which is readily attachable to supporting structure for theengine, for instance to a structural member of an aircraft wing, and thenozzle elements for varying the effective area of the outlet orifice arepivoted to the mounting structure so that on detachment of the mountingstructure the pivoting nozzle elements are also detached from theassociated jet pipe. In such an arrangement the mounting structure mayalso carry a ring element which mates with the end of the jet pipe onattachment of the mounting structure to the supporting structure, todetermine the effective throat area of the nozzle in the maximum orificearea position of the adjustable nozzle elements.

One embodiment of nozzle arrangement of this invention for use with agas-turbine engine will now be described With reference to theaccompanying drawings in which:

Figure 1 is an axial section through a part of the nozzle arrangement,the figure being divided into two parts 1A and 1B, of which the part 1Bis immediately. to the right of the part 1A, the line of junction of theparts being indicated by the reference 10,

Figure 2 is a section on the line IIII of Figure 1, and the figure hasthe plane of section of Figure l indicated on it by the line I -I,

Figure 3 is a view corresponding to Figure 2 but with the parts indiflierent positions,

Figure 4 is a section on the line IV-IV of Figure 1,

Figure 5 is a view to a larger scale of part of Figure 1,

Figure 6 is a section on the line VI--VI of Figure 5,

Figure 7 is a section on the line VII'-VII of Figure 6 and has the planeof section of Figure 5 indicated thereon by the line V---V,

Figure 8 is a section on the line VIII -VIII of Figure 1,

Figure 9 is a detail view,

Figure 10 is a section on the line X--X of Figure 9 "and has the planeof section of Figure 9'indicated on it by the section line IX--IX,

Figure 11 is a View corresponding to Figure 10 with the parts in anotherposition,

Figure 12 is a section on the line XII-*XII of Figure 8, and

Figure 13 is a diagrammatic View of part of the arrangement.

Referring first to Figure l, the jet nozzle arrangement illustrated issuitable for use either with a gas-turbine engine accommodated within anacelle forming part of an aircraft wing structure or with a gas-turbineengine accommodated within a fuselage and having its jet pipe opening toatmosphere through the after end of the fuselage.

In Figure 1, the jet pipe is illustrated as having an inner skin 20which defines the exhaust gas duct leading from the gas-turbine engineto the jet nozzle arrangement, and the inner skin has at its outlet enda frusto-conical portion 21 terminating in an annular end fitting 22having an axially-extending portion 22a of slightly larger diameter, andan outer skin 23 surrounding the inner skin 20 and held in spacedrelation thereto by means of a muif 24 to aflord a passage for coolingair. The outer skin 23 has welded on its downstream end anoutwardly-flanged end ring 25 and the mufl 24 is flared outward at itsdownstream end to provide a flange 24a which lies against the flange ofthe flanged end ring 25. Secured to the flanged end ring 25 is a furtherring member 26 having an axial extension 26a the purpose of which willappear below. The upstream end of muir 24 is formed as a number ofcircumferentially-extending strips 24b which are bent inward to havetheir free ends welded to the inner skin 20. The outer skin 23 of thejet pipe terminates at a position somewhat upstream of thefrusto-conical portion 21. r

The downstream end of the fuselage or nacelle in which the gas-turbineengine is located is indicated at 27 and there is indicated at 28 astructural member of the fuselage or wing structure, which member iscapable of carrying high loads. 7

The jetnozzle arrangement which is associated with the jet pipe 20, 23,comprises a mounting structure generally indicated at 29, by which thejet nozzle arrangement is attached to the aircraft structure injuxtaposition to the jet pipe, anda multiplicity of jet nozzle elementsby which the eflective area of the outlet orifice of the nozzlearrangement can be varied. The jet nozzle arrangement also COHlPl'iSESmotor means fOI moving the nozzle elements to vary the effective orificearea of the nozzle and the motor means is carried solely by the movingnozzle elements.

The mounting structure 29 comprises a pair of axiallyspacedannular endwalls 30a, 30b secured to an axiallyexten'ding inner wall 31, theupstream end 31a of :which is capable of sliding engagement with theaxial extension 26a of the ring member 26, and the downstream end 31b ofwhich is frusto-conical and is securedto the inner edge of thedownstream wall 30a. Another frustoconical member 310 connects the wall31 to the outer edge of annular wall 30a. The upstream end wall 30b isconnected with the axially-extending wall 31 by means of fabricatedsheet metal brackets 32, and these brackets 32 have projecting from themlugs 33 which project between pairs of lugs 28a on the structural member28 to enable the jet nozzle arrangement to be secured in position bymeans of pins or the like passing through aligned holes 34 in the lugs33 and the co-operating lugs 28a.

The mounting structure 29 also comprises an outer wall 35 adapted toform a smooth continuation of the fuselage or nacelle 27. The upstreamend of the wall 35 is formed with a radial, inwardly-directed flange 336having at its inner edge an axially-extending portion 37 to seat on anaxial flange 38 on the outer edge of the upstream wall 30b, and thedownstream edge of the wall 35 is headed as indicated at 39 and engagesa cylindrical seating 40 of a seal member 41, thepurpose of which willappear below. The seal member 41 is carried by a ring 41a secured to theouter edge of the downstream wall 30a.

The inner wall 31, as has been said, has sliding engagement with theaxial extension 26a of the ring member 26 and the wall 31 is radiallyspaced from the downstream portion of the inner wall 20 of the jet pipeand its conical end portion' 21, so affording a downstream extension ofthe annular air passages between the jet pipe walls 20, 23.

The mounting structure 29 also comprises a number of brackets 42 (seeFigures 5, 6, 7) fabricated from sheet metal, which brackets 42 supportbushes 43 to receive the ends of pivot pins 44 by which the nozzleelements areconnectedto the mounting structure 29.

The pivot pins 44 have heads 44a which limit the extent to which thepivot pins can pass in one direction through the bushes 43 anddisengagement of the pins 44 from the bushes 43 is prevented by flanges45 forming parts of union connections 46 in a pressure fluid system forsupplying pressure fluid tooperating rams (described below) for movingthe nozzle elements.

The nozzle elements are of two kinds, of which one kind, referred tohereinafter as the main nozzle elements, are indicated at 47, and ofwhich the other kind, which will be referred to as the sealing nozzleelements, are indicated at 48 (see especially Figures 2, 3 and 4).

The main nozzle elements 47 (of which there may for instance be 16) aredivided into two categories which alternate around the nozzle orifice,but each category comprises the following general structure.

Each main nozzle element comprises a load-bearing structure including anouter sheet-metal wall 49, a sheetmetal inner wall 50 and sheet-metalside walls 51 which are secured together to form an axially-extendingtapering tube-like structure. Each main nozzle element 47 also comprisesat its upstream end an end wall 52 and a forwardly-extending bracketstructure 53 carrying bushes 54, which fit between the pairs of bushes43 (see Figures 6 and 7) and also receive the pivot pins 44. Each mainnozzle element 47 is also strengthened internally at its upstream anddownstream ends by centrally-arranged tapering channel members 55 whichhave the base of the channel secured to the inner wall 50 and flanges551; secured to the outer wall 49.

The motor means for causing the main nozzle elements 47 to pivotrelative to the mounting structure 29 is in the form of fluid-operatedmotors such as hydraulic or pneumatic rams, and the motor structureforms part of the main nozzle elements 47.

The first category of main nozzle element 47 has located between itspair of members 55 a block 56 (Figures 1B, 2 and 3) having formed in itpressure fluid supply channels 57, and the block carries four ramcylinders 58. The ram cylinders 58 are arranged in two pairs, the onepair having a larger diameter than the other pair, and thelarger-diameter pair being disposed nearer the pivot for the nozzleelement than the smaller-diameter pair. One ram cylinder 58 of each pairis mounted on each side of the block 56 to extend towards an adjacentmain nozzle element 47. The outer end of each ram cylinder 58 is closedby a bored plug 59.

The other category of main nozzle element 47 has lo.- cated between itsmembers 55 a block 60 having therein a recess of part-spherical form toreceive part-spherical heads 61 of a pair of rocking arms 62 extendingcircumferentially from the block 6% through apertures 63 to form theouter ends of links which connect the nozzleelement 47 to the pistons 64which work in the ram cylinders 58 of the nozzle element next adjacentto it. The opposite ends of the links are formed by rods 65 having heads66 formed with part-spherical convex and concave surfaces which co:operate respectively with a part-spherical recess in thepiston 64 and adomed element 67 carried by a cap member 68 bolted to the head of thepiston 64. The stem 64a of the piston 64 is hollow to allow angularmovement of the rod 65 within it and the end of rod 65 remote from'thehead 66 is secured by a length-adjusting arrangement 69 to thecorresponding rocking arms 62. A spherical-surfaced plug 70 retains theheads 61 of the arms 62 in position in the recess and the plug 70 isretained in position within the block 60 by a plate 71 bolted to theblock 60. The plate 71 has a stem 72 carrying a cover plate 73 closingan aperture in the outer wall 49 of the nozzle element, .By removal ofthe cover plate 73 access can be had to the block 60.

It will be, appreciated that by supplying pressure fluid to one end ofthe ram cylinders 58, i. e. the end adjacent their supporting block 56,the nozzle elements 47 will be constrained to open up to increase theeffective area oiffthe' nozzle orifice and that on supply of pressurefluid to the opposite end of the ram cylinders 58 the nozzle elements 47will rock inwardly to reduce the effective orifice area of the nozzlearrangement.

Each main nozzle element 47 also comprises a removable protective wall74, the lateral edges 74asof which, as will best be seen from Figure 2,are joggled to co-operate with parts of the sealing nozzle elements 48ina manner to be described below. The. removable protective wall 74 hassecured to its outer surface an I-section member 75 the radially outerflange 75a of which is employed to connect the protective wall 74 to theinner Wall 50 of the nozzle element. The flange 75a engages in channelsformed by Z-section elements 76 secured to the inner surface of the wall50 and extending axially thereof (see particularly Figures 2 and 3). Theprotective wall 74 is retained against disengagement from its associatednozzle element 47 by means of a retaining member 77 which projects froma plate secured by set-screws 77a to the inner wall 50 of the nozzleelement 47 and which engages in a hole in the forward end of theradially-outer flange of the I.-section member 75 (see Figures 5.; and6). It will be. clear that since the wall 74 is only located adjacentits for-.

ward end, it is capable of expanding relatively to the load bearingstructure of the nozzle element 47.

The forward edge of the protective wall 74 bears against the downstreamedge of a seal member 78 carried by the load-bearing structure of themain nozzle. element 47 and the sealing element 78 is curved about thepivotal axis of the nozzle element and about the nozzle axis. The seal!ing element 78 co-operates with a sealing pad 79 provided externally ofa ring element 80 for the jet pipe, whichelement 80 is secured throughring members 81 to the end wall 30a of the mounting structure 29. j Theelement 80 is provided externally with a grooved land, 82 accommodatingasealing ring 83. which bears on the axial extension 2211 of the end ring22 carried by the frusto conical por= tion 21 of the inner wall of thejet pipe. It will be clear that when the jet nozzle arrangement is.being detached from the aircraft structure, the element 80 will beremoved with the jet nozzle arrangement. The sealing ring 83 preventsleakage of hot gas from the jet pipe.

Cooling air which has flowed between the walls 20, 23 of the jet pipe(see Figures 1A and 1B) and through the, space between the inner wall 31of the mounting structure 29 and the jet pipe wall passes outside thering element 80, through apertures in ring member 81, and outside thesealing member 78 into the spaces between the protective Walls 74 of thenozzle elements 47 and the inner walls 50 of their load-bearingstructure.

Each main nozzle element 47 also comprises an outer seal member 84 whichis curved about the pivot axis of its associated nozzle member and aboutthe nozzle axis and co-operates through its external surface with theseal member 41 above referred to.

The main nozzle elements 47 are constrained to move inwardlyandoutwardly to the same angular extents bylinking them together. Referringnow more particularly to Figures 113, 8 and 12, there are providedbetween each pair of main nozzle elements 47 a pair of links 85 oftriangular form which are pivoted both to the adjacent nozzle elements47 and to one another. Each link 85 is. pivoted to its associated nozzleelement 47 by having one side of it formed as an elongated boss. 85a toreceive a pivot pin 86 engaging in sockets 87 secured to. the edges ofthe outer and inner walls 49and 50 of the load-bearing structure of thenozzle element47. The apices of the triangulated links 85 are radiallyaligned and are interconnected through a ball and socket joint (Figure12), the ball 88 of the joint having a threaded stem 89 to engage in athreaded boss 90 on the apex of the outer link 85 and the socket of thejoint being provided in a boss 91 at the apex of the other link 85. Itwill be appreciated that this arrangement prevents relative radialmovement of adjacent nozzle elements 47 It will be appreciated that whenthe main nozzle elements 47 move outwardly their lateral edges tend tomove the joggled edge portions 74a of the protective walls 74 and it ispreferably arranged that in the minimum area position of the nozzleelements 47, 48 a substantially smooth frusto-conical wall is provided,the joggled portions 74a of the protective walls 74 being completelycovered by the inner sealing wall 92. The sealing strips 93 are retainedbetween flanges 92a at the edges of the inner walls 92 and flangedstrips 108 which are welded to the outer surface of the wall 92 (seeFigures 2, 3, 4, 6 and 8). The forward ends of the strips 108 have lugs108a (see Figure 6) which engage in notches in side flanges of theprotective wall 74 thereby to retain the inner sealing walls 92 axiallyin position. i

Referring now to Figure 4, it will be seen that the inner wall 92 of thesealing nozzle element 48 is supported from the adjacent main nozzleelements 47. The inner sealing wall 92 has secured to it a bracket 94having at its outer end a short, axially-extending T-section rail 95engaging in an undercut channel section member 96. The channel sectionmember 96 is carried at the inner end of a pivot pin 97 connecting apair of links 98 which are formed with sleeves surrounding the pin 97.The opposite ends of links 98 carry balls 99 received in sockets 100-mounted in the side walls 51 of the adjacent main nozzle elements 47. j

The outer end 101 of the pivot pin 97 of each sealing nozzle element 48is of T-form and engages an axiallyextending undercut channel formed bya. pair of Z strips 102 secured to the, inner side of the outer wall 103of the sealing nozzle element 48, thereby to support the outer wall 103.The lateral edges of each of the outer walls 103 of the sealing nozzleelement 48 overlie the outer walls 49 of the adjacent main nozzleelements 47 and, as the nozzleis opened and closed, slide over them.

The forward end of the outer wall 103 of each sealing nozzle element 48has secured to it a pair of Z-shaped lugs 104. (see Figures 9, 10, 11)which engage with the flanges 105 of a curved member 106 secured to themounting structure 29 and affording guides to control the movement ofthe forward ends of the sealing nozzle elements 48. The outer walls 103of the sealing nozzle elements 48 are retained against axialdisengagement from the associated main nozzle elements 47 by havingflanges of the Z-shaped lugs 104 engaged in notches 107 (Figure 9-).in.the circumferentially-spaced edges of the outer walls 49 of the mainnozzle elements 47. The guiding effect of the flanges 105 of the curvedmembers 106 is illustrated by Figures 10 and 11, the parts being shownin the maximum orifice area position in Figure 10 and in the minimumorifice areaposition in Figure 11.

The supply of operating pressure fluid to the rams 58 is efiected in anyconvenient manner and. in the arrangement illustrated is effectedthrough flexible supply pipes 109 leading from manifolds 110 in themounting structure 29 to the unions 46 which are carried on the endwalls 52 of themain nozzle elements 47 and through flexible pipes 111which lead from the unions 46 to the rams 58. Each set of rams 58 hasassociated with it a pair of supply pipes 109 from manifolds 110 and apair of supply pipes 111, and one of the supply pipes 111 leads to theblock 56 to deliver pressure fluid into the supply channel 57 and theother supply pipe 111 is provided with branches 111a which lead to theopposite ends of the rams 58. When the pressure fluid is suppliedthrough channel 57 to the adjacent ends of the rams 58 from one manifold110 the rams expand so opening up the nozzle, the maximum efiective areaof the 'nozzle elements being the position shown in full lines in Figure1B, and when the pressure fluid is supplied from the other manifold 110to theremote ends of the rams 58, the ram pistons'are retracted and thenozzle elements 47 are moved to reduce the effective area, the minimumarea position being shown in dotted lines in Figure 1B.

We claim:

' 1. A variable-area nozzle for a circular-section jet pipe comprisingcircular-section fixed structure at the down stream end of saidjet-pipe, two series of nozzle elements together forming an annularnozzle outlet, said nozzle elements alternating with one another aroundthe nozzle and said nozzle elements projecting downstream fromand beingpivotally connected to said fixed structure to pivot about axessubstantially tangential of said fixed structure, each nozzle element ofone of said series of nozzle elements having connected thereto a pair ofoppositelyfacing circumferentially-extending cylinders, and each nozzleelement of the other of said series of nozzle elements having connectedthereto a pair of oppositelyfacing circumferentially-extending pistonsone of which pistons slides in one of the pair of cylinders associatedwith the next adjacent nozzle element on 'one side and the other ofwhich pistons slides in one of the pair of cylinders associated with thenext adjacent nozzle element on the other side, means to supply pressurefluid sclectively to opposite ends of said cylinders thereby to causethe pistons to telescope in the said cylinders so that the nozzleelements pivot inwardly and to cause the pistons to move outwardly insaid cylinders so that the nozzle elements pivot outwardly respectively.

2. A variable-area nozzle as claimed in claim 1 comprising also aplurality of sealing elements, one between each pair of said nozleelements, and comprising means to support said sealing elements fromsaid nozzle elments.

' 3. A variable-area nozzle for a circular-section jet pipe comprising acircular-section fixed structure having an inner skin forming theboundary of the downstream end of the jet pipe and an outer skinsurrounding the inner skin, two series of nozzle elements togetherforming an annular nozzle outlet, said nozzle elements alternating withone another around the nozzle, and said nozzle elements being elongatedaxially of the nozzle and projecting downstream from saidcircular-section fixed structure and being pivotally connected to saidfixed structure at their upstream ends to pivot about axes substantiallytangential of said fixed structure, each of said nozzle elements havingan inner skin and an outer skin and intermediate structure extendingbetween and interconnecting said inner and outer skins of the nozzleelements, each nozzle element of one of said series of nozzle elementshaving mounted on its intermediate structure a pair of oppositely-facingcircumferentially-extending cyclinders, and each nozzle element of theother series of said nozzle elements having mounted on its intermediatestructure a pair of oppositelyfacing circumferentially extending pistonsone of which pistons slides in one of the pair of cylinders on thenozzle element of the one series next adjacent on one side, and theother of which pistons slides in one of the pair of cylinders on thenozzle element of said one series next adjacent on the other side, andmeans to supply pressure fluid selectively to opposite ends of saidcylinders, thereby to cause the pistons to telescope in the saidcylinders so that the nozzle elements pivot inwardly and to cause thepistons to move outwardly in said cylinders so that the nozzle elementspivot outwardly respectively. Y j

4. A variable-area nozzle as claimed in claim 3 comprising alsostabilizing means interconnecting each nozzle element and its nextadjacent nozzle element to constrain the nozzle elements to pivotthrough substantially equal angular extents.

5. A variable-area nozzle as claimed in claim 4, wherein the stabilizingmeans comprises a plurality of pairs of links, each pair extendingbetween an associated pair of adjacent nozzle elements, each link ofeach pair being pivoted at one end to a corresponding one of theassociated pair of nozzle elements and the links of each pair beingpivoted together in a manner to restrain relative radial displacement.

6. A variable-area nozzle as claimed in claim 5, where in the pivotalaxes between the links and the nozzle elements are radial to the nozzleaxis and each pair of links are connected through a ball and socketconnection.

7. A variable-area nozzle as claimed in claim 3, cornprising also anumber of sealing elements, one between each pair of said nozzleelements, and comprising means to support said sealing elements fromsaid nozzle elements.

8. A variable-area nozzle for a circular-section jet pipe of ajet-propulsion engine comprising a circular-section fixed structureadapted to be mounted on the downstream end of said jet pipe and beingsupported in gas-sealing relation with the end of the jet pipe,supporting structure externally of the jet pipe, a plurality of lugssecured to and projecting from said circular-section fixed structure,readily-detachable means securing said lugs to said supportingstructure, whereby the fixed structure of said nozzle may be readilydetached from the supporting structure of the engine, two series ofnozzle elements together forming an annular'nozzle outlet, said nozzleelements alternating with one another around the nozzle, each of whichnozzle elements projects downstream from said fixed structure and ispivotally mounted on the fixed structure to pivot about axessubstantially tangential thereto, whereby on detachment of the fixedstructure from said supporting structure the nozzle elements aredetached therewith, each nozzle element of one series of nozzle elementshaving connectedthereto a pair of oppositely-facingcircumferentially-extending cylinders, and each nozzle element of theother series of nozzle elements having connected thereto a pair ofoppositely-facing circumferentially-extending pistons one of whichpistons slides in one of the pair of cylinders associated with the nextadjacent nozzle element on one side and the other of i which pistonsslides in one of the pair of cylinders assopivot inwardly and to causethe pistons to move outwardly in the cylinders so that the nozzleelements pivot outwardly respectively.

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